Micro-electronic devices are used in a wide range of electronic products. These devices are typically manufactured from semiconductor (most often silicon) wafers. Using photolithography techniques, thousands of discrete electronic components, such as transistors, can be manufactured on a single silicon chip, with many silicon chips produced from a single wafer. The components on the chip, and the interconnections (or wiring) between them are formed in part with a metal, most often aluminum. However, recently, the semiconductor industry has moved towards using copper in place of aluminum, as copper provides several advantages. Consequently, copper metalization techniques are currently being actively researched.
Manufacturing of semiconductor devices with copper requires several critical cleaning steps. The first, a chemical-mechanical polishing step, is required after the copper interconnections or wiring have been formed, with an inlay process. This step uses a polishing slurry. When this polishing step is completed, the copper surfaces are contaminated with residual polishing slurry. The slurry must be removed from both the copper surfaces and the oxide surfaces.
A second cleaning step is required after the via etching step. Residues are left in the via hole after the plasma etching step, and must be removed.
In the past, strong alkaline solutions have been successfully used, with aluminum surfaces on semiconductor devices, to remove slurry after polishing steps, and also to remove residue in via holes after plasma etching. However, with semiconductor devices using copper, strong alkaline solutions are unacceptable and have not been used, because these solutions have an excessive etch rate on the copper, relative to the surrounding dielectric film. In addition, strong alkaline solutions form hydroxide film on the copper surface.
Accordingly, there is a need in the semiconductor industry for improved techniques for cleaning copper surfaces.